1. Field of the Invention
The present invention relates to a planarizing device and method, which is used for thinning and planarizing substrates by grinding and polishing the back surface of the semiconductor substrates in a preprocessing process of IC substrates.
2. Description of the Related Art
In a background planarizing device, semiconductor substrates are ground/polished for thinning and mirror finishing. Multiple substrate holder tables can retain substrates by vacuum suction are arranged in a lower side, and a rotating spindle comprising a rough grinding wheel, a rotating spindle comprising a finish grinding wheel, and a rotating spindle comprising polishing equipments is arranged on top of each of multiple substrate holder tables. A multi-joint transfer robot transfers the substrates that are stored in a substrate storage cassette to a temporary alignment table. Transfer equipment comprising transfer pads, which transfer substrates on the substrate holder table to the next processing stage, and a substrate cleaning device, is included with the planarizing device.
In one example, a device uses a plane grinding/polishing device comprising four sets of substrate holder tables. The tables can vacuum chuck five sheets of small diameter semiconductor substrates, and are arranged equally spaced on the same circumference from the shaft center of one index rotary table. The index rotary table is partitioned in a loading/unloading stage A, the first rough grinding stage B, the second finish grinding stage C, and a polishing stage D. It is typical to sequentially perform the process, which includes loading of the semiconductor substrates, with a multi-joint transfer robot to each substrate holder table on each stage accompanying the 90° rotation of the index rotary table, rough grinding process of the substrate back surfaces by rough grinding wheels, finish grinding of the substrate back surfaces by finish grinding wheels, mirror polishing by polishing pads and unloading by a transfer device. In this plane grinding/polishing device, each diameter of the rough grinding flat wheel, the finish grinding flat wheel and the polishing pads that are used, are larger than the diameter of the substrate holder table (for example, see Japanese Unexamined Patent Publication No. S60-76959).
As the diameter of the semiconductor substrates became larger up to 200 mm (8 inches), and one semiconductor substrate is placed on each of the four sets of substrate holder tables that are set on the index rotary tables, a planarizing device comprising a rough grinding diamond cup wheel, a finish grinding diamond cup wheel, and a polishing pad is provided. As shown in FIG. 1 and FIG. 2 of Japanese Unexamined Patent Publication No. 2000-254857, this planarizing device is a plane grinding/polishing device 10. Four sets of substrate holder tables 32, 36, 38, 40, which can vacuum chuck one sheet of the semiconductor substrate, are arranged on an index rotary table 34 equally spaced on the same circumference from the shaft center of the index rotary table 34. The index rotary table 39 is partitioned into the loading/unloading stage 17, the rough grinding stage 18, the finish grinding stage 20 and the polishing stage 22. The diameter of the rough grinding wheel 46, the finish grinding wheel 54, and the polishing pad 56 are 1-1.3 times the diameter of the substrate holder tables (for example, see Japanese Unexamined Patent Publication No. 2000-254857, which corresponds to U.S. Pat. No. 6,481,964 B).
In the planarizing device 510, which can plane grind/polish the substrate as shown in FIG. 5 and FIG. 6 of this application, from the front, 526 is a loading port (storage cassette) and an unloading port (storage cassette), 514 is a cassette storage stage, 528 is a semiconductor substrate, 512 is a base, 516 is a substrate alignment stage (temporary placement base), 523 is a polishing pad cleaning stage, 524 is a cleaning stage, 530 is a ceiling pendant multi-joint transfer robot, 558 is a travel rail, 597 is a transfer robot, 534 is an index rotary table, 537 is an axis of spindle of the index rotary table, 532, 536, 538, and 540 are substrate holder tables, 523 is a polishing pad cleaning device, and 527 is a polishing pad dressing stage.
Using this planarizing device 510, the process of grinding and polishing the back surface of the semiconductor substrate 528 is to seize and grip one sheet of the semiconductor substrate 528 stored in the loading port 526 in the cassette storage stage 514 with the hand 531 of the ceiling pendant multi-joint transfer robot 530, transfer them to the substrate alignment stage (temporary placement base) 516, and align the semiconductor substrate 528 there. After alignment, the semiconductor substrate 528 is again seized and gripped by the hand 531 of the multi-joint transfer robot 530, transferred to the substrate holder (vacuum chuck) 532 in the location of the loading/unloading stage 517 of the index rotary table 534, and seized and gripped by the substrate holder 532.
Next, the process includes rotating the index rotary table 534 90° clockwise, guiding the substrate holder 532, in which the semiconductor substrate 528 is placed at the location of the substrate holder (vacuum chuck) 536 of the first rough grinding stage 518, and rotating the rough grinding diamond cup wheel 46 there, and declining it to slit grind the back surface of the semiconductor substrate. When the thickness of the semiconductor substrate has reached the approximate desired thickness (for example, 100-250 μm, or 30-120 μm), the rough grinding diamond cup wheel 546 is elevated and removed from the back surface of the semiconductor substrate.
The rough ground semiconductor substrate 528 is transferred to the location of the substrate holder (vacuum chuck) 538 of the second finish grinding stage 520 by rotating the index rotary table 534 90° clockwise, and there, the finish grinding diamond cup wheel 554 is declined as it spins to slit grind to a thickness of approximately 10-20 μm from the back surface of the semiconductor substrate. When the thickness of the semiconductor substrate has reached the approximate desired thickness (for example, 80-220 μm, or 20-100 μm), the finish grinding diamond cup wheel 554 is elevated and removed from the back surface of the semiconductor substrate.
The finish ground semiconductor substrate 528 is transferred to the location of the substrate holder (vacuum chuck) 540 of the polishing stage 522 by rotating the index rotary table 534 90° clockwise, and there, by oscillating the rotating polishing pad 556, the surface of the finish ground substrate is polished to a thickness of 5-10 μm, which removes grinding defects. After polishing to a mirror surface, the polishing pad 556 is removed from the back surface of the semiconductor substrate.
The mirror polished semiconductor substrate 528 is returned to the first location of the substrate holder 532 of the loading/unloading stage 517 by rotating the index rotary table 534 90° clockwise, and being seized by the suction pad of the multi-joint transfer robot 597, it is transferred to the cleaning stage 524. There, the ground/polished surface is cleaned and dried. Next, after again being seized by the suction pad of the multi-joint transfer robot 597, it is transferred to the unloading port 526 and stored in the storage cassette 526.
After rotating each index rotary table 534 90° clockwise, loading and unloading of the semiconductor substrate, a rough grinding process, a finish grinding process, and a polishing process are performed at each stage. Moreover, the polishing pad 556 is cleaned in the polishing pad cleaning stage 523, the cleaned polishing pad 556 is dressed, and the chuck surface of the substrate is cleaned by the chuck cleaner 542 in the polishing pad dressing stage 527. In addition, the common machining allowance of planarized substrate layer by polishing is 8-13 μm, which is enough for grinding marks to disappear.
Although it depends on the manufacturer, currently, the diamond cup wheels used in grinding are cup wheels with 360 mesh grit grain size as the rough grinding diamond cup wheel 546, and cup wheels with 1,500 mesh grit grain size as the finish grinding diamond cup wheel 554 for plane grinding the back surfaces of the substrate, or cup wheels with 325 mesh grit grain size as the rough grinding wheel. Cup wheels with 2,000 mesh grit grain size as the finish grinding wheel for plane grinding the substrate back surfaces.
As a planarizing device resembling the planarizing device of Japanese Unexamined Patent Publication No. 2000-254857, a planarizing device is also proposed comprising four substrate holder tables (vacuum chuck) arranged on the same index rotary table, wherein one of the substrate holder tables is used as a loading/unloading stage for the substrates, and the remaining three substrate holder tables are each set up with a rotating spindle comprising a rough grinding diamond cup wheel, a rotating spindle comprising a finish grinding diamond cup wheel, and a rotating spindle comprising a dry polishing flat wheel. In this planarizing device, the rotating spindle comprising a dry polishing flat wheel is situated on the substrate holder table of the polishing stage allotted to the fourth polishing stage in a way possible to move in a direction perpendicular to the retention surface and is able to vacillate linearly (reciprocate) in a direction parallel to the retention surface (for example, see Japanese Unexamined Patent Publication No. 2005-153090, which corresponds to U.S. Pat. No. 7,022,000).
Moreover, an in-line system substrate back surface planarizing device is also proposed, comprising a substrate holder table (vacuum chuck) on an index rotary table for rough grinding and finish grinding of the back surface of a semiconductor substrate, a substrate holder table that is set separately from the index rotary table for polishing process, and a surface inspection device, which detects the presence of cracks or scratches on the semiconductor substrate at the time of transferring thinned semiconductor substrates to a mount device (for example, see Japanese Unexamined Patent Publication No. 2005-98773).
With a substrate diameter of 12 inches (300 mm) or 16 inches (450 mm), and a thickness of 20-50 μm, as is desired for production of extremely thin semiconductor substrates for the next generation, the creation of a grinding/polishing planarizing device, which is able to planarize the back surface of a sheet of semiconductor substrate faster (high throughput), and has a small footprint of the grinding/polishing planarizing device, is desired by semiconductor manufactures.
In a built-in system planarizing device, wherein the grinding/polishing process stated in Japanese Unexamined Patent Publication No. S60-76959, Japanese Unexamined Patent Publication No. 2000-254857 and Japanese Unexamined Patent Publication No. 2005-153090 are carried out on the substrate holder tables that are arranged in tiers on the same index rotary table, has the advantage of having a smaller footprint than that of the in-line system planarizing device. The grinding process described in Japanese Unexamined Patent Publication No. 2005-98773 is performed on the substrate holder on the index rotary table, and the polishing process is performed on the other substrate holder table, but its throughput is 12-13 sheets per hour with a 300 mm diameter substrate and it is inferior compared to 15-16 sheets per hour of an in-line system planarizing device. Moreover, because the grinding and the polishing are carried out on the same holder table, the holder tables and the processing tools get soiled faster, and there is a shortcoming of inferior planarization accuracy.
The planarizing device described in Japanese Unexamined Patent Publication No. 2000-254857 has advantages of being a little smaller and causes less damage to the processed substrate than the planarizing device described in Japanese Unexamined Patent Publication No. 2005-153090. The planarizing device of Japanese Unexamined Patent Publication No. 2005-153090, which uses dry polish for the polishing process has an advantage of being environmentally-friendly because there is no need to use an abrasive fluid slurry, but due to dry polishing without the use of abrasive slurry fluid, in order to prevent deterioration of the substrate from the heat generated while the substrate is processed, a procedure is necessary for cooling the substrates with cool air, and its footprint is a little larger than that of the planarizing device of Japanese Unexamined Patent Publication No. 2000-254857, and its throughput is inferior.
One aspect of the present invention embodies further improvement of the throughput of substrates with almost no increase in the footprint of the line system planarizing device, described in Japanese Unexamined Patent Publication No. 2005-98773.
In order to realize high throughput, the inventors focused attention on the fact that the polishing process is rate-controlled by the grinding process, and a shorter throughput than that of the planarizing device described in Japanese Unexamined Patent Publication No. 2005-98773 is enabled by dividing the polishing process into the first (rough) polishing process and second (finish) polishing process, in addition to having the first polishing process rate-controlled by the second polishing process.
One aspect of the present invention includes a planarizing device with high throughput as well as a limited increase in footprint and a system using the planarizing device for planarizing the back surface of the semiconductor substrate as its objectives.